Studies on molecular regulation of phagocytosis and activation of the NADPH oxidase in neutrophils. IgG- and C3b-mediated ingestion and associated respiratory burst independent of phospholipid turnover and Ca2+ transients.

The role of messengers derived from hydrolysis of phosphoinositides and other phospholipids, of the basal level of Ca2+i and of the increase in Ca2+i in phagocytosis and respiratory burst was investigated, using normal neutrophils and neutrophils Ca2(+)-depleted by pretreatment with Quin2/AM and EGTA. 1) Phagocytosis and respiratory burst in control neutrophils challenged with yeast opsonized with IgG or C3b/bi were associated with a stimulation of the production of inositol phosphates, diacylglycerol, phosphatidic acid, arachidonic acid, and rise in Ca2+i. 2) In Ca2(+)-depleted neutrophils (basal Ca2+i 10 to 20 nM) the phagocytosis of yeast-IgG was similar to that in control neutrophils, the respiratory burst was slightly depressed (-30%), while the increase in Ca2+i and production of inositol phosphates, diacylglycerol, and phosphatidic and arachidonic acid did not occur. 3) In Ca2(+)-depleted neutrophils the phagocytosis of yeast-C3b/bi was slightly lower than that in control neutrophils, and the respiratory burst, related to the same number of particles ingested, was depressed by about 60%, whereas the increase in Ca2+i and production of inositol phosphates, diacylglycerol, phosphatidic acid, and arachidonic acid release did not occur. These findings demonstrate that transmembrane signaling pathways involving the hydrolysis of phosphoinositides by phospholipase C and D and of other phospholipids by phospholipase C and Az, and the rise in Ca2+i are not essential processes for triggering the ingestion of yeast particles opsonized with IgG and C3b/bi and the activation of the NADPH oxidase.